completion-table-subvert

completion-table-subvert is a compiled Lisp function in `minibuffer.el'.
(completion-table-subvert TABLES1S2)
Return a completion table from TABLE with S1 replaced by S2.
The result is a completion table which completes strings of the
form (concat S1 S) in the same way as TABLE completes strings of
the form (concat S2 S).